Membrane topology of the integral membrane components, OppB and OppC, of the oligopeptide permease of Salmonella typhimurium

The oligopeptide permease of Salmonella typhimurium is a periplasmic binding protein-dependent transport system. Five gene products, OppABCDF, are required for the functioning of this transporter, two of which (OppB and OppC) are highly hydrophobic, integral membrane proteins and are responsible for mediating passage of peptides across the cytoplasmic membrane. OppB and OppC are each predicted, from their sequences, to span the membrane many times. In this paper we describe experimental evidence confirming these predictions using a combination of biochemical, immunological and genetic procedures. Each of these two proteins is shown to span the membrane six times, with the N- and C-termini both being located at the cytoplasmic face of the membrane. Opp is apparently a typical member of the ABC (ATP-binding cassette) superfamily of transporters. These findings, therefore, have general implications for the organization and function of other ABC transporters, including the human multidrug resistance protein and the product of the cystic fibrosis gene.